1. Field of the Invention
The present invention relates to an optically variable filter apparatus and its filter characteristic control method that are used in optical communication field and spectroscopic analysis field.
2. Discussion of the Related Art
Nowadays, an optically variable filter is widely used in various fields represented by the optical communication field and spectroscopic analysis field. Especially in the optical communication field, in order to meet increasing demand for an increase in transmission capacity in recent years, a higher transmission rate and new modification format have been actively researched and developed, and an optical network has become complicated. In such optical network, the optically variable filter capable of changing a light beam having a desired wavelength in optical signal is used. In such optical filter, in order to achieve optimum filtering with respect to the transmission rate and modification format of each optical signal, there is a demand for a function of dynamically controlling a filter center frequency and passband at an optical frequency level in addition to the conventional frequency selective function.
For example, US2006/0067611A1 discloses an optically variable filter using a two-dimensional reflection-type LCOS (Liquid Crystal On Silicon)-based liquid crystal element (hereinafter referred to as LCOS element) as a frequency selective element.